"One of the proponents of the bacteria theory was a co-author of
this paper (Jake Bailey of the University of Minnesota) and he
now agrees that the fossils do not represent a giant sulfur
bacteria," co-author Philip Donoghue, a professor of
palaeobiology at the University of Bristol, told Discovery News.

Images previously taken by Shuhai Xiao, a professor of geobiology
at Virginia Tech, reveal that many of the fossils from the
Dousantuo Formation in South China look like mini baseballs and
soccer balls.

With the bacteria hypothesis negated, that leaves a few
possibilities as to what these unusual fossils represent. One,
argued by Xiao and others, is that the fossils are of metazoan
embryos. If so, they would present one of the oldest records of
the animal evolutionary lineage.

Another theory is that the fossils are protists, which are
unicellular organisms lacking a definite cellular arrangement.
Protists include bacteria, algae, diatoms and fungi. Although not
animals, early protists may have given rise to the world’s first
animals and plants.

To test out the theories, Donoghue and his colleagues focused on
the possibility that the sports equipment-looking fossils were
bacteria. Living and decayed Thiomargarita, a modern
bacteria, were compared with modern embryos.

The researchers used a big particle accelerator in Switzerland to
study the fossils down to their most minute details -- just one
quarter of a micron. The extreme up-close look revealed that the
bacteria and the Doushantuo fossils are indeed very different.

Negation of the bacteria theory now strengthens the argument that
the fossils, be they embryos or some kind of protist, sit at the
base of the animal tree of life.

Donoghue doesn't think all animal life on Earth emerged from this
particular site. The location was "just chance," in terms of
preservation.

"It is the most awesome fossil deposit," he said. "Every single
grain is a fossil, and the deposit is 8 meters (over 26 feet)
thick."

Donoghue explained that there was a lot of dissolved phosphate in
the ocean at this now-China location during the Ediacaran Period.
The phosphate helped to preserve the fossils over the many
millions of years.

He said at least two animals have already been identified at the
site, but the finds are very controversial at present. One has
been called Vernanimalcula, meaning "small spring
animal,” referring to its appearance in the fossil record at the
end of what is known as the “Snowball Earth” freeze period.

Jun-Yuan Chen of the Nanjing Institute of Geology and
Paleontology at the Chinese Academy of Sciences and his
colleagues believe Vernanimalcula is the first known
bilateral animal, meaning the first with body symmetry. Donoghue
and others, however, dispute that claim.

Yet another rival for "world's oldest known animals" are fossils
from the Flinders Ranges of South Australia. They may also be
animals and date to nearly the same time period of around 570
million years ago.

Although China and Australia seem very disconnected today, that
may not always have been the case.

"According to paleogeographic reconstructions, South China and
South Australia were close to each other at the time, belonging
to a supercontinent called Gondwana," Maoyan Zhu, a scientist at
the Nanjing Institute, told Discovery News.

Findings concerning additional research on the Doushantuo fossils
are expected to be released soon, however, so the mystery over
what the fossils are may at last be resolved.